The present invention relates to information encoders which may be used for broadcasting systems, and in particular to information encoders used in digital broadcasting systems.
Digital audio broadcast is continually developing. For some time, DAB (digital audio broadcast) has existed for USW frequencies, and for a short time also DRM (digital radio mondial) has existed for long, medium or short waves.
Such broadcasting systems distinguish themselves by a certain number of data which have to be buffered before the broadcast or radio receiver, respectively, can start data output. When the radio listener switches on his radio receiver, this is not very problematic as the radio receiver simply starts reproducing a little later, and this interval is not perceived by the radio listener as especially disturbing. When the radio listener changes the program, however, the listener is used, from previous systems, to data being output immediately. With a digital broadcasting receiver this is, however, not possible as a certain amount of data has first of all to be stored again by the other program before a reproduction of this other program can be started. This delay will be perceived by the user as disturbing as it does not occur when he starts listening to the radio but while he is listening.
U.S. Pat. No. 6,842,724 B1 disclosed a method and a device for reducing the initial delay in data packet-based streaming applications or in a telecommunication network, like, for example, a local exchange carrier network or an inter-exchange carrier network or a local or global computer network. A program source, for example an audio and/or video data stream, is encoded and transmitted as two or more separate bit streams, for example sequences of data packets. The transmission of one of these bit streams is delayed by a given delay with regard to the transmission of the other bit stream. At the receive end of the transmission channel, the two or more bit streams are buffered by receiver buffers of different sizes, from which different time delays result when the content of the buffers is decoded. In particular, the time delay difference (inverse) corresponds to the relative delay times before transmission. For encoding, either a rewritable source encoding scheme or an embedded encoding scheme is used, wherein at least one of the individual bit streams is sufficient to generate a satisfying decoded signal, wherein adding the other bit stream will improve the quality of the decoded signal. Alternatively, the data streams may be several encoded representations of the program source having different bit rates, wherein encoded representations with a lower bit rate are transmitted with correspondingly greater delays.
In contrast to the transmission types described in the above-mentioned document, in which only the delay of a data package has to be considered, with digital broadcasting systems further challenges occur which result from the fact that the transmission channel is not a line-connected channel but a wireless transmission channel. A transmitter thus comprises a transmit antenna which emits radio waves which may be received and processed by a receiver comprising a receive antenna. Due to the fact that the transmission channel varies, which may be due to the system, and which may also result from the fact that the transmitter and especially the receiver is moving, a transmission channel may become better or worse and, in particular, so bad that the connection from the receiver to the transmitter is abruptly interrupted. In particular, as is generally the case with digital transmission, the connection below an SNR given by the system will simply be interrupted and there will be no so-called “graceful degradation”, i.e. a degradation of transmission quality taking place gradually, as occurs with analog radio broadcasting in an agreeable way. The interruption of the connection below an SNR given by the system (SNR=signal noise ratio) is a problem in particular with DRM, as DRM use short wave carriers which have a slowly varying SNR, which results in repeated failures.
With DAB, this threshold of receive quality and/or the SNR at which the connection is interrupted is problematic, as aligning the antenna or finding a good receive position becomes more difficult than in analog broadcasting and becomes even more complex in particular when the receiver is moving.